The amount of oil that can be recovered from California’s vast Monterey Shale formation using existing technology is far less than thought.

That’s according to a new federal estimate that found just 600 million barrels of oil can be drawn from the Monterey Shale, a 1,750-square-mile area extending from the agricultural Central Valley to the Pacific Ocean. That’s less than the previous estimate of 13.7 billion barrels of recoverable oil.

The Los Angeles Times reports the new estimate by the U.S. Energy Information Administration is expected to be publicly released next month.

Oil companies have used hydraulic fracturing, or fracking, to unlock oil from the Monterey Shale with mixed success.

The oil industry says it is hopeful new techniques will open up the formation.

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